1. Field of the Invention
The invention relates to a handover method, a system and a radio network controller.
2. Description of the Related Art
In cellular radio systems, radio coverage is achieved by radio cells, which typically have radiuses from tens of meters to a few kilometers. When a user moves from one cell to another, mobile equipment has to change to the radio frequency that is allocated to it in the new cell. This changing process is called a handover.
In WCDMA systems (Wide Band Code Division Multiple Access), like UMTS (Universal Mobile Telecommunication System), there are several different types of handovers, such as Intra-frequency handovers, Inter-frequency handovers and inter-system handovers. For performing a successful handover, user equipment has to make measurements to find out whether the signal of a base station (or B-node) to which it is connected is strong enough or would there possibly be a stronger signal in another cell.
Many of these measurements are made in a compressed mode (CM). The compressed mode means that transmission and reception are interrupted for a short period of time, typically for a few milliseconds, in order to perform measurements on the other frequencies. The data is thus compressed in the time domain. Frame compression can be done by lowering the data rate from higher layers, increasing the data rate by changing the spreading factor or reducing the symbol rate by puncturing.
The problem is that the compressed mode measurements cause quite a heavy load to a network and waste resources. The compressed mode measurements have the most noticeable effect on link performance if the terminal is at the cell edge.